Reference is made to the German Patent Application 199 07 858.0-33 from which the present application claims piority.
This invention relates a device for electrostatic deflection of a particle beam out of a primary beam direction for the purpose of scanning a plane spanned by two coordinates X, Y, in which multiple electrodes configured as deflection wires are connected to an activation circuit and are acted upon, depending on the activation, by modifiable deflection voltages. In this context the xe2x80x9cprimary beam directionxe2x80x9d is to be understood as the direction of the undeflected particle beam which intersects the origin of the coordinates X, Y; the deflection voltages are an equivalent for the deflection of the particle beam out of the primary beam direction in the direction of coordinate X or coordinate Y.
In particle beam equipment, for example in electron-beam and ion-beam exposure systems for exposing wafers, devices are necessary for deflecting the particle beam over the surface that is to be exposed.
In deflection devices of this kind, which are often also called deflection systems, the change in the direction of the particle beam is accomplished, in principle, by the influence of magnetic or electrostatic forces. Also known are deflection devices in which both principles are utilized in succession in the beam direction.
If the deflection of the particle beam is to take place quickly and accurately, electrostatic deflection systems are preferred. In such systems, multiple deflection electrodes are acted upon by different voltage potentials, thereby generating an electrostatic field that, depending on the change in voltage potentials and the activation of the deflection electrodes, acts on the particle beam so as to change its direction. Activation is accomplished in such a way that the particle beam is deflected out of a primary beam direction (which corresponds to the undeflected beam path) into a desired direction, and is guided as a function of the change in activation over a plane spanned by the coordinates X, Y.
Electrostatic deflection systems in which the deflection electrodes are configured in the form of wires that extend, over part of their length, parallel to the primary radiation direction, have recently been developed. One such deflection system is described in the German Patent Application DE 31 38 898 A1. In this, eight wires are arranged in radially symmetrical fashion around the primary beam direction. The wires are attached at their ends to insulators. The attachment positions on the insulators determine the location and orientation of the wires relative to the particle beam. The arrangement disclosed in DE 31 38 898 A1 of the wires with respect to the primary radiation direction is illustrated in FIG. 1 of the present specification.
One disadvantage of this device as compared to previously known deflection systems, in which electrodes were arranged distributed in the form of cylindrical or circular segments around the primary beam direction, is the fact that deflection sensitivity is lower, and moreover that greater complexity is involved in activating the electrodes, since mixed deflection potentials must be generated (cf. page 4 of DE 31 38 898 A1, lines 5 through 7). The mixed deflection potentials, for example U4=(Uy+Ux)/v2, are necessary so that the electrostatic field is at least approximately homogeneous.
The wire deflection system described above thus exhibits poorer practical value characteristics than the previously known existing art. As a result, its actual advantagexe2x80x94namely simplicity of manufacturexe2x80x94cannot be effectively utilized, especially for applications in which rapid and accurate deflection of the particle beam is desired.
Proceeding therefrom, it is the object of the invention to develop deflection systems of the kind described above in such a way that practical value characteristics are improved while retaining the advantages in terms of production engineering.
According to the invention, in deflection systems of this kind multiple deflection wires are linked into deflection grids, the deflection wires being joined to one another and to the activation circuit in such a way that an equivalent deflection voltage is always applied to all deflection wires belonging to one and the same deflection grid.
In a preferred embodiment of the invention, provision is made for multiple deflection grids to be allocated to the X coordinate and for the deflection wires of those deflection grids to be arranged symmetrically with respect to the Y coordinate; and/or for multiple deflection grids to be allocated to the Y coordinate and for the deflection wires of those deflection grids to be arranged symmetrically with respect to the X coordinate.
It has thereby been advantageously possible to achieve high field homogeneity even without the complex provision of mixed deflection potentials. It has moreover been possible, by suitable positioning of multiple deflection wires as will be explained in further detail below, to suppress in simple fashion the higher-order Fourier harmonics of the electrostatic potential, thus improving the field homogeneity even further. The application of the same potential to multiple deflection wires has advantageously resulted in an elevated deflection sensitivity for the entire deflection system.
A particularly preferred embodiment of the invention provides for two deflection grids to be allocated in each case to the X coordinate and to the Y coordinate. The deflection grids allocated to the X coordinate are located opposite one another symmetrically with respect to the Y coordinate; the deflection grids allocated to the Y coordinate are located opposite one another symmetrically with respect to the X coordinate. A voltage potential xc2x1UX is provided between the deflection grids allocated to the X coordinate, and a voltage potential xc2x1UY is provided between the deflection grids allocated to the Y coordinate. The deflection of the particle beam out of the primary radiation direction is effected as a function of the change in the voltage applied to the deflection grids.
In further embodiments of the invention, at least two deflection wires of one and the same deflection grid are arranged at different spacings from the origin of the X and Y coordinates. In other words, the spacings between the deflection wires and the undeflected particle beam are of different magnitudes for at least two deflection wires of a deflection grid. In this context, provision can advantageously be made for the cross-sectional center points of all the deflection wires to be distributed on circumferential lines of multiple concentric circles k1, k2 through kn, these circles also being oriented concentrically with respect to the coordinate origin or the undeflected particle beam. As a result, the spacings of the deflection wires that belong to one and the same deflection grid are defined with respect to the undeflected particle beam via the radii r1, r2 through rn of circles k1, k2 through kn.
An embodiment that is particularly favorable in terms of field homogeneity results, for example, if a total of four deflection grids are provided, each deflection grid being constituted from six deflection wires, the deflection wires of all the deflection grids being arranged distributed on circumferential lines of three circles k1, k2, k3 having radii r1 less than r2 less than r3, and each of circles k1, k2 and k3 being occupied by two deflection wires of each grid.
In this context, the ratio of the radii r1:r2:r3 should be approximately 1:1.1:1.21. The arc length b1 between the two deflection wires of a grid on circle k1, the arc length b2 between the two deflection wires of a grid on circle k2, and the arc length b3 between the two deflection wires of a grid on circle k3 should be related to one another as 8:1:14.
It is advantageous in this context to embody arc length b1 within the range of values from 5 mm to 10 mm. Deflection voltages xc2x1UX and xc2x1UY should lie in the range of values up to xc2x1100 volts.
Very good results in terms of field homogeneity and deflection sensitivity have been obtained therewith, especially in applications in electron-beam lithography. With this embodiment, field inhomogeneitiesxe2x80x94considered in a section perpendicular to the undeflected particle beamxe2x80x94are optimally suppressed; in particular, the second- to seventh-order Fourier harmonics of the electrostatic potential are reduced toward xe2x80x9czero.xe2x80x9d
Other ratio values and orders of magnitude can of course also be selected, and differing results will then naturally be obtained. It is moreover also conceivable for circumferential lines of circles not, or not exclusively, to be selected as the basis for the fundamental structure of the arrangement, but rather for other geometrical figures (e.g. rectangles, octagons, and the like) to be taken as the basis. What is always essential in terms of function in this context is that the deflection wires are to be arranged on these circumferential lines symmetrically with respect to the X coordinate axis and/or symmetrically with respect to the Y coordinate axis.
The material to be provided for the deflection wires is preferably gold, platinum, tungsten, aluminum, or copper, or also an alloy of one or more of these metals with silicon. The diameter of the deflection wires should be between 10 xcexcm and 200 xcexcm.
In addition to the advantageous effect in terms of improving field homogeneity and enhancing deflection sensitivity, the simple configuration also results in good technological conditions for high manufacturing accuracy of a deflection device of this kind.
The deflection device according to the present invention is preferably usable for equipment for generating exposed patterns on wafers or masks in the semiconductor production process. The advantageous effect found here is in particular the fact that the deflection wires present a small surface area to the particle-based optical radiation used for exposure, so that charging, which could result in undesirable effects on the direction of the particle beam, is largely suppressed.
An additional advantage is the fact that because of the relatively small wire surface area, the field strength resulting from charging of a deflection wire with the respective deflection current is high, so that undesired charging is rapidly dissipated.
A further essential advantage of the arrangement according to the present invention is the fact that because of the plurality of deflection wires, voltage potentials that are directed from outside onto the deflection system are largely blocked in terms of their effect on the particle beam.
Because of the broad range of possible variations in terms of the arrangement of the thin wires, aberrations in particle optics can be suppressed substantially better than is the case with known solutions having few deflection electrodes. With a deflection system according to the present invention that has twenty-four deflection wires, for example, the inhomogeneities of the electrostatic field in the section plane perpendicularly through the primary beam direction are optimally suppressed for the reasons already set forth.
It is important, in the manufacture of the device according to the present invention, that the positional deviations of the deflection wires from their predefined positions be minimized so that the aberrations caused by positional inaccuracies also assume a negligible magnitude in terms of optical imaging quality. Because the assemblies are uncomplicated, however, this is easy to bring about.